Method and apparatus for mixing gases



Dec. 7, 1965 R. P. NEWTON, JR

METHOD AND APPARATUS FOR MIXING GASES 4 Sheets-Sheet l Filed March 29, 1963 ATTORNEYS www Dec. 7, 1965 R. P. NEWTON, JR

METHOD AND APPARATUS FOR MIXING GASES 4 Sheets-Sheet 2 Filed March 29, 1963 R O T m V m ATTORNEY5l Dec. 7, 1965 R. P. NEWTON, JR 3,221,757

METHOD AND APPARATUS FOR MIXING GASES Filed March 29, 1963 4 Sheets-Sheet 5 d2 4f 45 f5 y s` 50 4(15 L .fr d'4 i. 62

79 f M5. M /02 LZ@ /04 ya /EU/ BY I l W Mg ATTORNEYS Dec. 7, 1965 R. P. NEWTON, JR 3,221,757

METHOD AND APPARATUS FOR MIXING GASES Filed March 29, 1965 4 Sheets-Sheet 4 7%? 1%? 7' PPO/@w- K /g I:,/

V l l INVENTOR ATTORNEYSI United States Patent O 3,221,757 METHOD AND APPARATUS FR MIXING GASES Robert P. Newton, Jr., R0. Box 506, Orangeburg, S.C. Filed Mar. 29, 1963, Ser. No. 269,124 9 Claims. (Cl. 137-9) This invention relates to gas mixing apparatus, and particularly to such apparatus adapted for mixing two or more gases in predetermined proportions and delivering Vthe mixture irrespective of flow rates within predetermined limits, and is a continuation-in-part of Serial No. 854,424, tiled on November 20, 1959, now abandoned.

It is frequently necessary to mix two or more gases to provide a desired mixture, and to maintain a flow of the mixed gases to meet specified requirements. One example of such use is so-called peak shaving and standby plants which provide for the mixing of propane and air to obtain a mixture having burning characteristics comparable to natural or other gas of a primary supply to provide an auxiliary or emergency gas source. By having such an auxiliary supply source, urban gas companies are able to augment their normal supply to accommodate abnormal peak loads, and industrial plants can take iadvantage of the cheaper rates offered by such companies to those willing to have their normal supply cut oi in times of peak load.

A number of systems have been proposed and used for this purpose, but their use has been limited due to the fact that all incorporate delicate and complicated instruments which require the attention of specially skilled mechanics. As the systems are used only at infrequent intervals, usually of short duration, suitable service personnel cannot be kept available. Still another factor attributing to the lack of widespread use is the need for closer proportion control and quicker response to variations in demand load than former systems could supply.

The general object of the present invention is to provide gas mixing apparatus which will be low in cost, as compared to other systems, and which will provide accurate control insofar as proportions are concerned with almost instantaneous response to supply and demand variations.

A more specific object of the invention is to provide apparatus of this nature wherein the gases are given equal pressure drops across orifices of fixed size to give the desired proportion of each gas to be mixed.

Another object of the invention is the provision of apparatus wherein the flow of one of the gases to be mixed is influenced and adjusted in accordance with the fiow of the other gas.

Yet .another object is to provide apparatus of this nature assembled and mounted as a unit, ready for installation in an emergency, or auxiliary, system.

A further object is to provide mixing apparatus which is entirely automatic in operation, and can be manually or automatically started and stopped, and which may be designed to automatically cut off in the event of abnormal conditions which would affect the desired output.

Still another object is the provision of la mixing unit having means to change the relative proportions of the gases being mixed by the pressing of a button on a control board.

A still further object of the invention is to provide an improved means for continuously mixing the proportioned gases to prevent turbulence in the mixing area.

Another object is to provide means to maintain substantially constant temperature relationship between gases being mixed.

Other objects of the invention will become apparent from the following description of practical embodiments thereof, when taken in conjunction with the drawings 3,221,757 Patented Dec. 7, 1965 ICC which accompany, and iform part of, this specification.

In the dnawings:

FIGURE 1 is a top plan view of a gas mixing unit constructed in accordance with the principles of the present invention;

FIGURE 2 is a side elevation of the unit shown in FIGURE 1;

FIGURE 3 is an end elevation of the unit;

FIGURE 4 is a diagrammatic view of the operating components, and their interconnection, of a system which is slightly different from that shown in FIGURES 1 to 3, inclusive;

FIGURE 5 is .a diagrammatic view of the basic system, shown in its simplest form;

FIGURE 6 is a diagrammatic view of a portion of a system in which one -of the orifice valves can be controlled from a remote point to vary the feed ratio;

FIGURE 7 shows in diagram a system in which an outside air supply is used as a source of instrument air;

FIGURE 8 is a schematic illustration of part of the system with means to provide for heat exchange between the entering gases; and

FIGURE 9 is a section through an improved mixing chamber, showing the gas lines entering the chamber.

In general, the invention is concerned with the mixing of gases, such as propane and air, and the controlling of the proportions of the mixture by first controlling the pressures of the gases to be mixed and dropping the pressures of the controlled gases in numerically equal amounts through proper sized orifices prior to mixing. This, and the using of the pressure of one gas as a control medium for the pressure of the other provides an extremely accurate control both of pressures and mixture ratio.

Referring to the drawings in detail, and first adverting to FIGURE 5 there is shown schematically the basic lay-out of the present system, and the principle upon which the other illustrated forms of the invention are founded.

FIGURE 5 shows two gas lines 1 and 2, which lead from suitable sources of gas under pressure. For purposes of this description, Ithe line 1 will be considered a propane line and the line 2 an air line. The propane 1 has a regulator 3 controlled by a pilot 4 and, spaced from the regulator, a manually adjustable valve 5 which, after adjustment, acts as a fixed orifice. The air line includes a regulator 6, having a pilot 7, and a valve 8 to provide a fixed orifice in the air line. The two lines merge beyond the valves 5 and 8, `to permit the gases of the two lines to mix and liow through a feed line 9. A regulator 10 in the feed line controls the rate of flow of the mixed gases from the apparatus. Regulator 10 may be a manually operable valve, or it may be automatic and controlled by a pilot 11.

The purpose of the regulators 3 and 6 is to admit gas from the source lines in such quantities as to create equal pressures in the two downstream lines. The valves 5 and 8 are set so that they form fixed orifices to cause a significant pressure drop in each line prior to mixing'. This pressure drop is a significant amount so that in the event of slight variation between the pressures of the two lines there will be but inconsequential change in the ratio of the final mixture.

If, for example, propane is available at eighty pounds pressure and air at fifty-five pounds pressure, and it is desired to mix the propane and air in predetermined proportions, the regulators 3 and 6 can be set to reduce the pressure and deliver the propane and air at forty-five pounds. The valves 5 and 8 will be initially adjusted and set so that flow of propane and air in their respective lines will be in desired proportions to one another and a further and significant equal pressure drop is obtained. This second pressure drop can bring the pressures in the two lines to thirty pounds, for example. The propane and air, being reduced in numerically equal amounts through valves 5 and 8 will mix in predetermined proportion in the line 9 and be fed at a desired rate through the regulator 10. The rate of flow through the regulator 10 will have a denite eiect upon the degree of pressure drop across the valves 5 and 8 by affecting the pressure in the lines downstream of the valves 5 and 8.

In order to maintain close control over the pressures in the line and have the system respond instantly to pressure changes, or pressure differentials, one of the regulators is controlled by a known force counteracted by the pressure in the line that regulator controls. The other regulator is controlled by its own line pressure counteracted by the pressure of the other line to make the regulator instantly responsive to differential pressure in the two lines. To accomplish this result, the propane line has its regulator 3 controlled by a diaphragm type pilot 4 which is spring loaded to the degree necessary to obtain the desired pressure in the propane line. The reduced line pressure is applied to the opposite side of the diaphragm to balance the spring load when the line pressure is'proper. The line pressure is fed back to the pilot through a line 12 connecting the propane line and the pilot. The pilot 7 of the regulator 6 is connected to the air line through line 13, and this pressure is balanced by the pressure of the propane line through line 14 bridged from line 12 to the pilot 7. Thus, in the example given, the spring loading of pilot 4, the propane line pressure as fed to the pilot through line 12, the air line pressure as applied to pilot 7 through line 13 and the propane line pressure imposed on pilot 7, through line 14 will be identical when4 the system is functioning properly and the pressures in the propanel and air lines have been reduced to be equal and at the predetermined level. Any uctuation from this condition will place one or both of the pilots, as the case4 may be, in an unbalanced condition to adjust the regulators to correct the condition.

As mentioned above, the feed regulator 10 may be manually or automatically controlled. If it is automatic, it may be controlled by line pressure, rate of flow of the propane-air mixture, rate of ow of propane, rate of flow of air, or any other desired factor. For purposes of illustration, it is shown as controlled by the line pressure of the mixed propane and air on the outlet side of the regulator. This is done by preloading the pilot 11 and imposing the line pressure in opposition through the line 15.

The above described system can be modified for various uses. More than two gases can be mixed, if desired, by adding one or more lines to the system shown. Other improvements can be added to the basic system to make it more exible in operation, and to adapt it to manufacture and installation as a unitary system connectible to existing sources of supply and to utility lines or equipment to be supplied.

FIGURESY 1, 2 and 3, show a mixing unit which includes as a part thereof the system described. The unit is mounted upon a base 16 having a horizontally positioned rectangular frame 17 supported upon legs 18. The frame is constructed of channel members, welded at the corners, and the legs are mounted directly beneath the corners. Suitable braces 19 are positioned diagonally at the corners to stiien the legs and to support cross-members 20 upon which part of the mixing apparatus is mounted. Inverted U-shaped arbors 21 have their vertical legs secured to the horizontal frame 17 and are placed at spaced intervals along the frame to provide perches upon which the major part of the apparatus is mounted. i

The mixing apparatus includes a propane line 22 and an air line 23, Veach of which has a pair of legs con-` nected by a U-tting with the legs being parallel to one another and lying at upon the arbors 21 and being secured to them. One leg of each line has an upturned elbow at its end, the elbow 24 forming a means for connecting the propane line to a source of propane supply, and the elbow 25 a means to connect the line 23 to a source of air supply. The ends of the opposite legs are connected by fittings 26 and 27 to branch lines 28, 29 and 30, 31. The branch lines, in turn, are all connected to a fitting 32 on one end of a gas mixing and outlet line 33.

Each of the several lines is provided with one or more valves to open and close the line and to regulate the pressure and flow in the line. The air line 23 has a manually operable cut-off valve 34 adjacent the inlet elbow 25` This permits the line to be closed olf when the unit is not in operation, and will be opened and left open when the unit is to be put in use. A check valve 35 is mounted adjacent the shut-olf valve to prevent back ow of air in the line.

Next along the line is a safety valve to cut oi the line in the event of predetermined malfunction of a selected part of the system. The valve is shown as a conventional air motor valve 36 adapted to close automatically upon a drop in pressure of the air supply below a selected level. An air line 37 connects the valve to a connector plate 38, and a line 39 leads from the plate to a control panel 40. An air pressure sampling line 41 is tapped into the air line 23, and connects to the plate and control panel. When the air pressure drops below a predetermined minimum, a valve (not shown) operated by pressure in the line 41, will disconnect lines 37, 39 from a source of instrument air (not shown) to permit valve 36 to operate to Shut down the supply of air under pressure.

The initial control of pressure in the air line is obtained by means of a regulator valve 42, which is mounted in the line and controlled by pilot 43. The pilot is actuated by the pressure of the gas in the propane line by means of a pipe 45, leading from a propane sampling line 46 tapped into the propane line downstream from the propane regulator valve. This pressure on the pilot is opposed by the pressure in the air line beyond the regulator 42, which pressure is imposed on the pilot through line 44.

The propane line has cut-off and check valves 47 and 48, similar to the valves 34 and 35 in the `air line. A safety motor valve 48 is included in the propane line. The valve will be used and controlled to automatically shut off the propane line simultaneously with the valve 36 in the event of malfunction of the system.

The propane pressure is first reduced by means of a regulator valve 49 controlled by `a pilot 50. The pilot is spring loaded and this pressure is opposed by the propane line pressure beyond the regulator by means of the ine 46.

The branch lines are also controlled by valves. The several lines have shut-oit valves 52, 53, S4 and 55, and manually adjustable valves 56, 57, 58 and 59 which provide after adjustment the xed orices through which the gases pass. By having two lines for each gas feed line, it is possible, by opening and closing the several lines, to change the capacity of either gas line to increase or decrease the ow rate and still obtain significant pressure drops across these orifices.

It is to be noted that the propane and air lines 22 and 23 are mounted upon the arbors 21 while the mixing line 33 is supported upon the cross-members 20 of the frame. This places the gas lines above the mixing line so that gravity and gas ow can be utilized to drain olf condensate which may form in the line to avoid its collection and possible freezing in the line.

The fitting 32 is enlarged at its upper end, into which the branch lines empty, to form a mixing chamber 60 for the propane and air owing from the open branch lines.

Thus, smooth blending of the gases and free flow of the mixed gas into the line 33 is obtained.

The flow of mixed gas through the line 33 is determined by a regulator valve 61 which is controlled by a pilot 62. The pilot is loaded in a predetermined amount by instrument air entering through line 63, the air pressure being opposed by t-he outlet pressure of line 33 by means of a sampling line 64 connected to line 33 and to pilot 62.

The mixing line may be provided with a manually operable shut-off valve 65 if desired. The line ends with a flange for coupling to the line to be supplied with mixed gas.

The pressures of the various lines, and at different points along the lines, may be sampled and shown on instruments indicated at 66 on the control panel. The sampling lines are shown at 67. The control panel may also have appropriate control buttons 68 for starting and operating the unit. Signal lights 69 are shown for indicating whether or not the various parts of the unit are functioning properly.

I-t will be obvious that the unit just described will operate in substantially the same manner as the basic system previously described. It has the added advantage of additional automatic controls, and means to permit changing the range of the flow r-ates of the gases without changing the settings of the fixed orifices while maintaining significant pressure drops. The fact that the apparatus is made self-contained and mounted upon a base provides a unit which can be shipped and installed quickly and easily by relatively unskilled labor. The use of a control panel through which the control lines pass allows the control point to be remote from the unit and out of the zone of dangerous operation. It is to be noted that all of the controls on the mixing unit are air or gas operated so that no electrical equipment with its attendant fire, or explosion, hazard is present.

In FIGURE 4 is shown a diagrammatic layout which combines the principles of the previously described apparatus with additional equipment to provide for automatic control and push-button change-over to provide several mix proportions without changing the setting of any of the manually operable valves.

The system includes propane line 70 from a source of supply and air line 71 from a source of air under pressure. The two lines empty into a mixing line 72 which can be coupled into the line to be fed. Propane line 70 has a cut-off valve 73, check Valve 74, safety motor valve 75, pilot controlled regulator valve 76 and manually controlled valve 77 which provides the fixed orifice. Motor valve 7S is operated by instrument air through line 78 from a source 79. Flow through line 7S is controlled by a pressure valve 90 inserted in the line and closed by pressure in a line 81 which leads from a pressure differential detector 89 bridged across the air and propane lines. The regulator 76 is controlled, as before, by spring loading and by propane line pressure through line 82.

The air line 71 has shut-ofi" valve 83, check valve 84, motor safety valve 85, regulator valve 86 and orifice valve 87. The motor valve is operated by instrument air through the line 88 under control of the pressure differential detector 89 which controls switch 90 in line 78. Regulator 86 is controlled by airline pressure beyond the regulator through line 91 aud by the propane line pressure beyond the regulator through line 92 tapped into line 82.

The flow of mixed gases through the line 72 is controlled by regulator valve 93 which has its pilot 94 spring loaded and balanced by feeding pressure in the line 72 through line 95.

The system of FIGURE 4 differs from those previously described in that a plurality of additional lines are provided to bridge the orifice valve 87 in the air line. The bridge lines 97, 98 an-d 99 each contain a manually operable valve which can be set to define a fixed orice, and an automatic Valve which will open and close the individual lines. The orifice valves 100, 101 and 102 are in 6 the lines 97, 98 and 99, respectively, and the same lines contain the motor valves 103, 104 and 105. The motor Valves are connected to the instrument yair supply through lines 106, 107 and 108 and controlled by push-button valves 109, 110 and 111. The push-button valves will be mounted upon a control panel similar to the one previously described and positioned remotely from the unit.

The orifice valves 100, 101 and 102 may be adjusted so that each has the same setting and the motor valves may be operated to open one or more of the bridge lines to additively supplement the valve 87 and increase the capacity of the air line, or each of the valves 100, 101 and 102 may be set at a different orifice opening and the several bridge lines opened selectively to permit their respective orifices to augment the orifice 87. Thus, the ratio of air to propane may be changed at will. This provides a very flexible system.

The use of pressure differential between the propane and air lines as a safety control provides an accurate and simple means to prevent continued operation of the system under improper conditions. Such a safety control could not be used were it not for the fact that the basic mixing method and apparatus provides equal pressures in the propane and air lines. So long as the pressures in the two lines are equal, the system is functioning properly. If variation beyond a predetermined amount occurs improper mixing will result. By utilizing the differential as means to actuate the safety shut-ofi valves, the system will be automatically shut down in the event of malfunction anywhere in the system, as such malfunction will cause a pressure differential to occur.

In FIGURE 6, there is shown a portion of the basic system illustrated in FIGURE 5, but with an adjustable valve used to provide the orifice in one line, so that the ratio of the mix can be changed. In the embodiment shown, the adjustable valve 112 is shown in the air line 113. Propane line 114 has a fixed orifice 11S as before. The two lines empty into a mixing line 116.

Valve 112 is a motor valve, and is controlled by a variable regulator 117 which may be located at a control panel, or lsome other remote location. One side of the motor valve pilot is connected by line 118 with a switch source of instrument air, and the regulator 117 is in that line. The instrument air acts against a constant spring pressure in the valve pilot.

Valve 112 may be a two position valve, having limits of movement, so that two predetermined orifice settings can be obtained. It will be clear that an operator by manipulation of the variable regulator 117 at a remote point may change the orifice in the air line and thus change the propane-air ratio.

Frequently, it is desired to have the system adjust to compensate for slight differential in the pressures in the system air and propane lines. This -may not be a sufiicient pressure drop to operate the regulator valve properly, as the springs used in the regulators as balance loads are strong and require substantial force to overcome. This may be corrected by using an outside air source for a supply of instrument air, and controlling the instrument air in accordance with requirements. Such an arrangement is shown in FIGURE 7.

In FIGURE 7, a line 119 to be controlled includes a motor valve 120. The motor valve has a pilot 121, and this is controlled by a pilot regulator 122. A line 123, from a source of air outside the system, leads into the central chamber 124 of the pilot regulator to be controlled by the diaphragm head assembly 125 through valve 126. Movement of the head assembly up and down opens and closes valve 126 to open and close line 123 to chamber 124. The chamber is connected to the motor valve pilot 121 by line 127 so that outside air can be used to offset the motor valve pilot balance spring and move the valve when a line diferential occurs. The diaphragm head assembly movement is controlled by differential pressures in the air and propane lines. In the embodiment shown, line 128 connects the regulated air line (not shown) with the bottom chamber of 4the pilot regulator, and line 129 connects the regulated propane line 119 to the top chamber of regulator 122. With this arrangement, a pressure drop in the propane line will cause the diaphragm head assembly 125 of the pilot regulator to rise and open valve 126 to release air pressure to the motor valve pilot 121, to open the motor valve to increase propane flow in line 119 to bring the air and propane lines into balance. When the lines come into balance, the pressures in the top and bottom chambers of the pilot regulator will equal and the head assembly will have returned to valve closing position. Through the use of this arrangement, sufficient air pressure can be made available to insure operation of the motor valve.

It is of utmost importance to accurate control of the air and propane mixture that the relative temperatures of the elements remain constant. Temperature change will cause volume change, and if the relation of the temperatures of the air and propane does not stay substantially the same, the nal mixture will vary. In order to maintain a -substantially constant temperature relationship, the equipment shown in FIGURE 8 may be used.

The principal added element of the arrangement shown in FIGURE 8 is a heat exchanger 130. This may include a shell 131 through which the propane line 132 passes. This line may run straight through the shell, or may be a coil 133 as shown. The air line 134 connects to the shell near one end to provide an inlet 135 and adjacent the opposite end to provide an outlet 136. Suitable bafiies 137 may be located within the shell to provide a tortuous path for the air for maximum contact with the propane line. It will be apparent that temperature change in either the propane or air line will result, through heat exchange, in a change in the temperature of the other. Thus, the temperature relationship will be maintained.

FIGURE 9 illustrates a mixing coupling which will serve as a connector between the air, propane and mixed gas lines, and allow the incoming air and propane to mix smoothly and progressively with gas fiow, without turbulence or back pressure. The coupling 138 is in the form of a T, having a central stem 139 for connection to the mixed gas line 140 and branches 141 and 142 extending at right angles from the stem. The air and propane lines 143 and 144, respectively, are of smaller diameter than the branch lines 141 and 142 and project through caps 145 and 146 which close the ends of the branch lines. Air and propane lines 143 and 144 project through the branch lines of the T-coupling and have their outlet ends 148 and 149 bent to lie within the stem portion of the T-member. Thus, outlet ends 147 and 148 are generally parallel to one another and to the axis of the stem 139 of the mixing coupling, and the incoming air and propane will be projected into the stem in side-byside relation and longitudinally of the stem. By reason of this, the gases to be mixed will flow into the coupling stem while moving in the same direction, gradually and smoothly mixing without creating back pressure or turbulence. In this arrangement, the coupling stem serves as the mixing chamber.

It is believed that the operation of the several embodiments of the invention disclosed will be clear from the above description and that no additional review of the operation will be necessary.

While in the above practical embodiments of the invention have been disclosed, it will be understood that the details of construction shown and described are merely by way of example and the invention may take other forms within the scope of the appended claims.

What is claimed is:

l. The process of accurately mixing fluids of different physical characteristics to obtain a mixture of predetermined constant physical characteristics :which comprises, entraining separate streams of fiuids under source pressures, adjusting the pressures of the streams to substantially the same valve, maintaining the adjusted pressure substantially constant in a first one of the separate streams, controlling the pressure in a second one of the separate streams in accordance with the pressure in the first stream, reducing the pressure in each stream in substantially equal and significant amounts, and combining the separate streams of reduced pressure into a single comingled stream.

2. The process of mixing fluids as claimed in claim 1, and controlling the fiow rate of the combined stream.

3. Apparatus for accurately mixing fluids of different physical characteristics to obtain a mixture of predetermlned constant physical characteristics comprising, a first fluid conduit, a second fiuid conduit, and a conduit for mixed fiuids connected to the first and second fiuid conduits at a common point and into which the first and second conduits empty, an automatic valve in each of said conduits, means to provide a set orifice in each of said first and second conduits between the automatic valves and the connection of the first and second conduits and the mixed fluid conduit, means to operate the automatic valve in the first conduit inrresponse to variations in pressure in the first conduit between the automatic valve and the set orifice .in the first conduit, and means to operate the automatic valve in the second conduit in response to pressure differential between the first and second conduits between the automatic valves and the set orifices therein, the means to provide a set orifice in at least one of said conduits bemg an automatic valve, and means located remote from the apparatus to control the automatic valve providing the set orifice to change the set orifice to vary the ratio of the mix.

`4. Apparatus for accurately mixing fluids of different physical characteristics to obtain a mixture of predetermined constant physical characteristics comprising, a first fluid conduit, a second fluid conduit, and a conduit for mixed fluids connected to the first and second fluid conduits at a common point and into which the first and second conduits empty, an automatic valve in each of said conduits, means to provide a set orifice in each of said first and second conduits between the automatic valves and the connection of the first and second conduits and the mixed fluid conduit, means to operate the automatic valve in the first conduit in response to variations in pressure in the first conduit between the automatic valve and the set orifice in the first conduit, and means to operate the automatic valve in the second conduit in response to pressure differential between the first and second conduits between the automatic valves and the set orifices therein, and the means to operate each automatic valve including, a pilot for each automatic valve, a pilot regulator having a valve therein responsive to pressure differentials in the said conduits, a line interconnecting the pilot regulator valve and the pilot of its respective automatic valve to provide operating fiuid for the automatic valve, and means interconnecting the pilot regulator valve with a source of fluid under pressure.

5. Apparatus for accurately mixing uids of different physical characteristics to obtain a mixture of predetermined constant physical characteristics comprising, a first fluid conduit, a second fluid conduit, and a conduit for mixed fiuids connected to the first and second fluid conduits at a common point and into which the first and second conduits empty, an automatic valve in each of said conduits, means to provide a set orifice in each of said first and second conduits between the automatic valves and the connection of the first and .second conduits and the mixed fiuid conduit, means to operate the automatic valve in the first conduit in response to variations in pressure in the first conduit between the automatic valve and the set orifice in the first conduit, and means to operate the automatic valve in the second conduit in response to pressure differential between the first and second conduits between the automatic valves and the set orifices therein, a heat exchanger having a shell and a tubular conduit through the shell, one of said first and second conduits including the tubular conduit through the shell and the other of said first and second conduits including the shell of the heat exchanger, said heat exchanger being located in the respective conduits upstream from the means providing the set orifices.

6. Apparatus for mixing two fluids of different characteristics to obtain a liuid of predetermined physical characteristics comprising, a base structure, a first fluid conduit and a second fluid conduit mounted upon the base in side by side relation, a conduit for mixed fluids mounted upon the base at a level below that of the first and second conduits, a vertically arranged -connector including a mixing chamber coupled to the first and second conduits and to the mixed duid conduit, an automatic valve in each of said conduits, a manually adjustable Valve to provide a set oriiice in each of said first and second conduits between the automatic valves and the connector, means to operate the automatic valve in the first conduit in response to variations in pressure in the first conduit between the automatic valve and the manually adjustable valve in the first conduit, and means to operate the automatic valve in the second conduit in response to pressure differential -between the said variations in pressure in the first conduit and pressure variations in the second conduit between the automatic valve and the manually adjustable valve therein.

7. Apparatus for mixing two fiui-ds of different characteristics as claimed in claim 6 wherein there is means to control the automatic valve in the iiuid mixing line in response to 4pressure Variations in the fluid mixing line downstream of said Valve.

8. Apparatus for mixing two fluids yof different characteristics as claimed in claim 6 wherein there is at least one conduit bridging the manually adjustable valve in one of said first and second conduits, a manually adjustable valve in the bridging conduit, and means in the bridging conduit to close and open that conduit.

9. Apparatus for mixing two fluids of different characteristics as claimed in claim 6 wherein there is at least one conduit bridging the manually adjustable valve in each of the first and second conduits, a manually adjustable valve to provide a set orifice in each bridging conduit, and means in each bridging conduit to close and open that respective conduit.

References Cited by the Examiner UNITED STATES PATENTS 1,092,204 4/ 1914 Cross.

1,213,159 l/1917 Dalen 137-98 X 1,452,265 4/'1923 Collins et al 137-606 X 1,667,113 4/1928 Heidbrink 137-98 X 2,309,848 2/1943 King 137-4895 X 2,341,177 2/1944 Cope 137-98 2,379,633 7/1945 Garretson 137-98 X 3,115,892 12/1963 Brewer 137-501 FOREIGN PATENTS 498,685 l/1939 Great Britain.

MARTIN P. SCI-IWADRON, Acli/Lg Primary Examiner.

M. CARY NELSON, Examiner. 

1. THE PROCESS OF ACCURATELY MIXING FLUIDS OF DIFFERENT PHYSICAL CHARACTRISTICS TO OBTAIN A MIXTURE OF PREDETERMINED CONSTANT PHYSICAL CHARACTERISTICS WHICH COMPRISES, ENTRAINING SEPARATE STREAMS OF FLUIDS UNDER SOURCE PRESSURES, ADJUSTING THE PRESSURES OF THE STREAMS TO SUBSTANTIALLY THE SAME VALVE, MAINTAINING THE ADJUSTED PRESSURE SUBSTANTIALLY CONSTANT IN A FIRST ONE OF THE SEPARATE STREAMS, CONTROLLING THE PRESSURE IN A SECOND ONE OF THE SEPARATE STREAMS IN ACCORDANCE WITH THE PRESSURE IN THE FIRST STREAM, REDUCING THE PRESSURE IN EACH STREAM IN SUBSTANTIALLY EQUAL AND SIGNIFICANT AMOUNTS, AND COMBINING THE SEPARATE STREAMS OF REDUCED PRESSURE INTO A SINGLE COMINGLED STREAM. 